This application claims priority, under 35 USC 119, of earlier-filed Japanese Application HEI 5-14076, filed Jan. 29, 1993.
The present invention relates to torque generator steering control units, and more particularly, to such devices in which a relatively low torque input is translated into a relatively high torque steering output, with the aid of a source of pressurized fluid.
Torque generators of the type to which the present invention relates have been in commercial use for many years, have been commercially successful, and are illustrated and described in greater detail in U.S. Pat. Nos. Re. 25,291 and 4,936,094, both of which are assigned to the assignee of the present invention and are incorporated herein by reference.
In the typical prior art torque generator of the type illustrated and described in above-incorporated U.S. Pat. No. 4,936,094, even a relatively low torque input is sufficient to deflect the leaf springs disposed between the spool (attached to the input shaft) and the sleeve, thus initiating the flow of fluid through the valving. In other words, at almost any level of input torque, the prior art torque generator operates as a fluid pressure assisted steering unit.
Furthermore, in the prior art torque generator, there are typically at least three sets of splines disposed in series between the input shaft and the output shaft, with each set of splines introducing a certain amount of looseness or backlash into the mechanical connection between the input shaft and the output shaft. In addition, the torque generator of U.S. Pat. No. 4,936,094 also includes a drive pin and bifurcated drive shaft arrangement, well known to those skilled in the art, which adds further to the backlash between the input and output shafts.
U.S. Pat. No. 4,169,515 discloses a steering unit which is an attempt by those skilled in the art to provide a steering unit having a hydraulic power assist which imparts its power assistance directly to the output shaft. However, the power assist device in the steering unit of the above-identified patent is a sliding vane device which either produces too little torque for a given package size, or conversely, results in too large a package size for the amount of torque produced. In other words, the device of the '515 patent does not amplify power to the same level, for a given package size, as an orbiting gerotor type "torque generator", as that term will be defined subsequently.